When holding a Level 4/4 map, there is a ~0.25 second entity lag about every second. I noticed it after making a minecart track as minecarts are effected most obnoxiously, but later realized that all mobs are also effected. A level 3/4 map does not have this issue. My server resources to not appear to be maxed out. 1-player only so far.
Framing the map does not cause the problem, I have a wall of 4 level 4/4 maps with smooth performance, only when I am holding one and it is updating does the entity lag take place.